Exemplary embodiments relate to an image sensor. In particularly, exemplary embodiments relate to a complementary metal oxide semiconductor (CMOS) image sensor for compensating dark shading, i.e., a difference in dark current locally occurring within a pixel array, by including a dark pixel for detecting a local dark current in an active pixel block and a method thereof.
A sensor including a pixel array, which senses effective physical quantities, such as light intensity, temperature, mass, or time, and outputs an electrical signal based on the sensing result, is used in various fields. In particular, an image sensor measuring a captured image of an object is applied to various fields.
In a related art, a dark frame is captured before or after capturing an exposed frame. Then, in the related art, the dark frame is subtracted from the exposed frame. However, in the related art, this requires a mechanical shutter and an image buffer, and measures a dark signal at a different time from a real image.
In a related art, a dark signal is evaluated in an image using a model (such as incorporating information from covered pixels placed at sensor peripherals). However, in the relate art, a dark signal isn't uniform over a pixel array. Therefore, measuring the dark signal at peripherals of the pixel array isn't enough. Even if a model is setup that will accurately approximate the dark signal all over the pixel array but this involves calibration for each sample, which is an expensive process (i.e., the dark signal becomes significant at high ambient temperatures).
In a related art, a complicated mechanical setup (e.g., mirrors and dedicated sensors) are required. However, in the related art, complicated mechanical setups are expensive and inappropriate for small cameras (DSC and mobile), due to a size limitation.
In a related art, partially shielded pixels in a pixel array are incorporated. However, in the related art, partially shielded pixels don't support a measurement of a dark signal.